This invention relates to an exhaust system for a small planing boat and more particularly to an improved exhaust system for a watercraft propelled by an inboard engine, such as a jet propelled watercraft.
In marine propulsion units, it is a common practice to employ the cooling water from the body of water in which the watercraft is operating to cool the powering internal combustion engine. In order to facilitate discharge of the cooling water and also to provide silencing, it has been the practice to discharge the cooling water into the exhaust system of the engine. This procedure is used not only with inboard engines, but also with outboard motors that are water cooled.
Although the aforedescribed system is effective to provide silencing, it has some disadvantages. Specifically, because of the addition of water to the exhaust gases, the use of sound deadening materials such as fiberglass packing cannot be employed. Hence, many conventional forms of exhaust silencing utilized with other types of engines cannot be employed with marine propulsion engines.
Another way in which the exhaust gases in a marine propulsion unit are silenced is by discharging the exhaust gases through an underwater exhaust gas discharge. However, this method of silencing has certain disadvantages caused primarily due to the different speeds at which the watercraft may operate. For example, if the exhaust gases are discharged into the body of water in which the watercraft is operating at a low level when the watercraft is operating at low speeds, then the discharge may be too high and above the water when operating at high speeds. Alternatively, the low discharge may give rise to too high a back pressure in the exhaust gases.
With many types of inboard engines, it is the practice to discharge the exhaust gases through the transom of the watercraft. However, this type of discharge presents the problems as noted in the preceding paragraph.
In connection with jet propelled watercraft, it has been proposed to discharge the exhaust gases into the tunnel in which the jet propulsion unit is positioned. This internal discharge of the exhaust gases can improve silencing efficiency. However, the previously proposed discharges of this type have been partially submerged when operating at low speeds and have been above the water and thus provide minimal silencing when at high speeds.
In addition to the problems aforenoted in connection with exhaust gas discharge from a marine propulsion unit, many types of watercraft, because of their sporting nature, frequently may become overturned or capsized. When this occurs, there is a danger that water in the exhaust system may flow into the engine through its open exhaust ports. This presents obvious difficulties upon restarting.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a marine propulsion unit.
It is a further object of this invention to provide an exhaust system for a marine propulsion unit that provides good silencing under all running conditions.
It is a further object of this invention to provide an exhaust system for a jet propulsion unit which will provide excellent silencing under all running conditions.
It is another object of this invention to provide an exhaust system for a small watercraft that embodies a silencing device and which silencing device also acts as a water trap to trap water in the even the watercraft becomes inverted and to prevent the water from flowing to the engine through the exhaust ports either when inverted or when righted.